Researchers find carcinogenic chromium-6 in Palisades, Altadena fire cleanup zones

A carcinogen with potentially serious impacts on human health was found in neighborhoods in the months after the 2025 Los Angeles County wildfires and may have spread to communities as far as 6 to 9 miles downwind of the fire zones, according to newly published work by researchers at UCLA and UC Davis.

The peer-reviewed research - "Airborne hexavalent chromium nanoparticles detected around cleanup zones for the 2025 Los Angeles wildfires" - was published in the journal Nature Communications Earth & Environment. The study, which is still subject to final revisions, was published to give early access to its findings to other researchers and the public.

Specifically, the researchers found that the airborne chromium was predominantly in a carcinogenic oxidation state two months after the fire, with measurements below the National Institute for Occupational Safety and Health workplace exposure limit but above the U.S. Environmental Protection Agency's screening levels for indoor air.

Additional calculations using models for wind-carried contaminants suggest that chromium-containing nanoparticles may have traveled 6 to 9 miles downwind from the cleanup zone, entering communities well away from the neighborhoods where the fires hit the hardest. In Los Angeles, for example, that includes communities as far from the Palisades fire as the southern San Fernando Valley to the north and as far east as Beverly Hills and West Hollywood.

"Monitoring near wildfire cleanup zones is warranted to ensure that concentrations decay to background levels over time," said study co-author Michael Jerrett, professor in the Department of Environmental Health Sciences at the UCLA Fielding School and the Jonathan Fielding Chair in Climate Change and Public Health. "Residents living adjacent to wildfire cleanup zones should take steps to reduce their exposure by using indoor air filters and limiting outdoor exercise in the fire zones until conditions return to safe levels."

The January, 2025 blazes in Los Angeles County, in both the Pacific Palisades-Malibu area in western Los Angeles, adjacent to the Santa Monica Mountains, and the Altadena-Pasadena communities in the foothills of the San Gabriel Mountains, claimed at least 31 lives and damaged or destroyed more than 18,000 structures, according to the County.

Read more about the report on the UCLA Fielding School of Public Health website.